Dérivée seconde de $$$\csc{\left(x \right)}$$$
Calculatrices associées: Calculatrice de dérivées, Calculatrice de dérivation logarithmique
Votre saisie
Déterminez $$$\frac{d^{2}}{dx^{2}} \left(\csc{\left(x \right)}\right)$$$.
Solution
Trouvez la dérivée première $$$\frac{d}{dx} \left(\csc{\left(x \right)}\right)$$$
La dérivée de la cosécante est $$$\frac{d}{dx} \left(\csc{\left(x \right)}\right) = - \cot{\left(x \right)} \csc{\left(x \right)}$$$ :
$${\color{red}\left(\frac{d}{dx} \left(\csc{\left(x \right)}\right)\right)} = {\color{red}\left(- \cot{\left(x \right)} \csc{\left(x \right)}\right)}$$Ainsi, $$$\frac{d}{dx} \left(\csc{\left(x \right)}\right) = - \cot{\left(x \right)} \csc{\left(x \right)}$$$.
Ensuite, $$$\frac{d^{2}}{dx^{2}} \left(\csc{\left(x \right)}\right) = \frac{d}{dx} \left(- \cot{\left(x \right)} \csc{\left(x \right)}\right)$$$
Appliquez la règle du facteur constant $$$\frac{d}{dx} \left(c f{\left(x \right)}\right) = c \frac{d}{dx} \left(f{\left(x \right)}\right)$$$ avec $$$c = -1$$$ et $$$f{\left(x \right)} = \cot{\left(x \right)} \csc{\left(x \right)}$$$:
$${\color{red}\left(\frac{d}{dx} \left(- \cot{\left(x \right)} \csc{\left(x \right)}\right)\right)} = {\color{red}\left(- \frac{d}{dx} \left(\cot{\left(x \right)} \csc{\left(x \right)}\right)\right)}$$Appliquez la règle du produit $$$\frac{d}{dx} \left(f{\left(x \right)} g{\left(x \right)}\right) = \frac{d}{dx} \left(f{\left(x \right)}\right) g{\left(x \right)} + f{\left(x \right)} \frac{d}{dx} \left(g{\left(x \right)}\right)$$$ avec $$$f{\left(x \right)} = \cot{\left(x \right)}$$$ et $$$g{\left(x \right)} = \csc{\left(x \right)}$$$ :
$$- {\color{red}\left(\frac{d}{dx} \left(\cot{\left(x \right)} \csc{\left(x \right)}\right)\right)} = - {\color{red}\left(\frac{d}{dx} \left(\cot{\left(x \right)}\right) \csc{\left(x \right)} + \cot{\left(x \right)} \frac{d}{dx} \left(\csc{\left(x \right)}\right)\right)}$$La dérivée de la cosécante est $$$\frac{d}{dx} \left(\csc{\left(x \right)}\right) = - \cot{\left(x \right)} \csc{\left(x \right)}$$$ :
$$- \cot{\left(x \right)} {\color{red}\left(\frac{d}{dx} \left(\csc{\left(x \right)}\right)\right)} - \csc{\left(x \right)} \frac{d}{dx} \left(\cot{\left(x \right)}\right) = - \cot{\left(x \right)} {\color{red}\left(- \cot{\left(x \right)} \csc{\left(x \right)}\right)} - \csc{\left(x \right)} \frac{d}{dx} \left(\cot{\left(x \right)}\right)$$La dérivée de la cotangente est $$$\frac{d}{dx} \left(\cot{\left(x \right)}\right) = - \csc^{2}{\left(x \right)}$$$ :
$$\cot^{2}{\left(x \right)} \csc{\left(x \right)} - \csc{\left(x \right)} {\color{red}\left(\frac{d}{dx} \left(\cot{\left(x \right)}\right)\right)} = \cot^{2}{\left(x \right)} \csc{\left(x \right)} - \csc{\left(x \right)} {\color{red}\left(- \csc^{2}{\left(x \right)}\right)}$$Simplifier:
$$\cot^{2}{\left(x \right)} \csc{\left(x \right)} + \csc^{3}{\left(x \right)} = \left(-1 + \frac{2}{\sin^{2}{\left(x \right)}}\right) \csc{\left(x \right)}$$Ainsi, $$$\frac{d}{dx} \left(- \cot{\left(x \right)} \csc{\left(x \right)}\right) = \left(-1 + \frac{2}{\sin^{2}{\left(x \right)}}\right) \csc{\left(x \right)}$$$.
Donc, $$$\frac{d^{2}}{dx^{2}} \left(\csc{\left(x \right)}\right) = \left(-1 + \frac{2}{\sin^{2}{\left(x \right)}}\right) \csc{\left(x \right)}$$$.
Réponse
$$$\frac{d^{2}}{dx^{2}} \left(\csc{\left(x \right)}\right) = \left(-1 + \frac{2}{\sin^{2}{\left(x \right)}}\right) \csc{\left(x \right)}$$$A